On Tue, Nov 03, 2020 at 03:34:00PM +0200, Sakari Ailus wrote:
> Add a printk modifier %p4cc (for pixel format) for printing V4L2 and DRM
> pixel formats denoted by fourccs. The fourcc encoding is the same for both
> so the same implementation can be used.
...
> +static noinline_for_stack
> +char *fourcc_string(char *buf, char *end, const u32 *fourcc,
> + struct printf_spec spec, const char *fmt)
> +{
> + char output[sizeof("(xx)(xx)(xx)(xx) little-endian (0x01234567)")];
I would add a comment that there is another possibility, i.e. big-endian, but
it occupies less space.
> + char *p = output;
> + unsigned int i;
> + u32 val;
> +
> + if (fmt[1] != 'c' || fmt[2] != 'c')
> + return error_string(output, end, "(%p4?)", spec);
> +
> + if (check_pointer(&buf, end, fourcc, spec))
> + return buf;
> +
> + val = *fourcc & ~BIT(31);
> +
> + for (i = 0; i < sizeof(*fourcc); i++) {
> + unsigned char c = val >> (i * 8);
> +
> + /* Weed out spaces */
> + if (c == ' ')
> + continue;
> +
> + /* Print non-control ASCII characters as-is */
> + if (isascii(c) && isprint(c)) {
> + *p++ = c;
> + continue;
> + }
> +
> + *p++ = '(';
> + p = hex_byte_pack(p, c);
> + *p++ = ')';
> + }
I guess above loop can be still optimized, but I have to think about it.
> + strcpy(p, *fourcc & BIT(31) ? " big-endian" : " little-endian");
> + p += strlen(p);
> +
> + *p++ = ' ';
> + *p++ = '(';
> + /* subtract parenthesis and the space from the size */
This comment misleading. What you are subtracting is a room for closing
parenthesis and NUL.
> + p = special_hex_number(p, output + sizeof(output) - 2, *fourcc,
> + sizeof(u32));
I would go with one line here.
The (theoretical) problem is here that the case when buffer size is not enough
to print a value will be like '(0xabc)' but should be rather '(0xabcd' like
snprintf() does in general.
> + *p++ = ')';
> + *p = '\0';
> +
> + return string(buf, end, output, spec);
> +}
--
With Best Regards,
Andy Shevchenko
